There are a number of applications that will make sure you're on time for your appointments and never forget your best friend's birthday, but they're not all created equal. Here's a look at five of the most popular desktop calendaring applications.

Last week we asked you which calendar app you used to keep track of important dates. You answered the call, and now we're back to highlight the ones you nominated.

If you have a Mac, you already have iCal. The app integrates tightly with other Mac OS apps and goes mobile on your iOS device, and supports notifications in advance of appointments. Since it uses the .ics calendar standard, you can quickly import or export to and from other services like Google Calendar. iCal also allows you to share calendars via Mobile Me, but with iCloud coming, that may change.

Some of you went out of your way to nominate Outlook because it's what you use at work, others said you prefer it for your personal appointments as well. Regardless, Outlook offers built-in tools to keep your appointments organized by type, integrates with your email, and when combined with Exchange is a powerhouse that supports resource booking, appointment locations, free/busy times, and more.

While it's not technically a desktop calendaring app, Google Calendar is clearly the go-to calendar service for many of you. It's free, Web-based and accessible anywhere, and if you have a Google account you already have access to it. Adding appointments is easy from the Web interface or from Gmail, and most other applications can sync with it.

Thunderbird is already our favorite email client for Windows, but when you add Lightening, the Mozilla Foundation's calendaring plug-in, you get a utility that allows you to read messages, stay on top of appointments, and import/export your calendar to other apps. Mozilla has woefully neglected lightning, but if you like Thunderbird for mail, Lightning will keep your calendar organized.

Rainlendar is the ultimate "out of the way" calendaring utility. The app's lightweight widgets sit on your desktop and warn you of upcoming appointments and to-dos without draining system resources. There are countless skins for it, so you can find a look that works for you. Pay €10 (approx $14) and you'll get a "pro" license that supports syncing with Google Calendar, Outlook, and Remember the Milk, among others.

Now that you've seen the top five, it's time to vote for an all out winner.

This week's honorable mention goes out to BusyCal for Mac, which offers mobile calendar sync, multi-user sharing and editing, and support for syncing to Google Calendar. BusyCal will set you back $49.99 for a single user license, but it's a great alternative to Exchange or Google Calendar for groups looking to share calendars.

Did we miss your favorite? Do you want to make the case for your favorite? Sound off in the comments. Photo by John Lanman.